It is common practice to chrome plate many different types of industrial parts which are made of stainless steel in order to give the parts a bright, shiny surface. By way of example, automotive vehicle body moldings, door handles, and other functional or decorative parts are chrome-plated for appearance purposes. Frequently, such parts are made of stainless steel to prevent rusting.
In commercial practice, chrome plating stainless steel parts typically is accomplished by initially buffing the stainless steel to achieve a high luster and then electroplating with chromium to retain the high luster and to make the finished surface more durable. In the past, stainless steel parts have been electroplated with nickel before the chromium electrolytic plating step. But, the adhesion between the nickel plating and the steel part has been erratic. Further, the red rust resistance of the nickel plated part has been erratic.
It has been understood by those skilled in the art that proper adhesion and good red rust resistance could not be consistently achieved when electroplating nickel over stainless steel. Particularly, conventional pre-plating surface treatment followed by conventional plating has not been effective in producing sufficient chemical bond between the stainless steel surface and the nickel coating. This has been especially true in the case of bright annealed stainless steel. Thus, there has been a need for a process to strongly adhere nickel plating to an annealed stainless steel workpiece and to maintain red rust resistance of the plated part.
This invention relates to an improvement in the nickel-plating process and, more particularly, in the electrolytic acid surface-treating step used in the process of nickel plating stainless steel, which causes the plating to better adhere to the stainless steel while, simultaneously, not destroying the red rust resistance of the stainless steel surface.